1. Field of the Invention
This invention relates to manipulations of (i.e. a patterning technique for) electroconductive film comprising a monomolecular film or monomolecular built-up film and to said electroconductive film having been patterned. More particularly, the present invention relates to a method for manipulation an electroconductive film to change its electrical characteristics in accordance with a desired pattern and also to the electroconductive film prepared by such manipulation. The present invention also relates to a method for providing an electrode on an electroconductive film, particularly a method for providing an electrode at the terminal ends of an electroconductive film having a constitution with electroconductive layers and insulating layers being laminated alternately. The present invention further relates to a method for providing an electrode, particularly a method for providing an electrode by forming a peeled portion on an electroconductive film such as monomolecular film or monomolecular built-up film, etc., provided on a support by exposure to energy irradiation and providing an electrode at said peeled portion. Further, the present invention relates to a method for manipulating (or patterning) by polymerization of a specific compound in an electroconductive film of a monomolecular film or monomolecular built-up film.
2. Description of Related Art
Generally, a molecule having a hydrophilic group and a hydrophobic group therein with an adequate balance between the both groups (amphiphilic balance) forms a monomolecular layer with the hydrophilic group directed toward on the water surface When the planar density of this monomolecular layer is increased, the intermolecular interaction is intensified to give a two dimensional "condensed film (or a solid film)". The condensed film can be transferred as a monomolecular film onto the surface of a substrate such as glass, and by repeating this operation multiple times onto the same substrate, a monomolecular built-up film can be formed on the substrate. The method for preparing such monomolecular film or its built-up film is known as the Langmuir-Blodgett method (hereinafter referred to as LB method) and is described in detail, for example, in Sin-jikken Kagaku Koza (New Course of Experimental Chemistry) 18 Surface and Colloid" pp. 498-507, published by Maruzen
It is also known that certain organic molecules can be formed into a monomolecular film or its built-up film according to the LB method or the like to give an electroconductive thin film. Alternatively organic molecules in monomolecular film or its built-up film can be polymerized to give an electroconductive polymer film
Further, it has been recently reported that an amphiphilic charge transfer complex having a long alkyl group as the hydrophobic site such as bis-tetracyanoquinodimethane docosylpyridinium: ##STR1## which is an organic compound with tetracyanoquinodimethane (TCQN) being as the electron acceptor can be formed into a monomolecular built-up film according to the LB method (Preprint of the 51th Autumn Annual Meeting of Chemical Society of Japan, p. 490). This monomolecular built-up film was observed to have an electroconductivity as high as 0.1 S/cm in the direction parallel to the 10.sup.-14 S/cm in the direction perpendicular thereto, thus behaving as an insulator in that direction.
When an organic thin film is prepared according to the LB method employing such molecules the electron cloud of the charge transfer complex constituting the hydrophilic site in the condensed film state will be greater, whereby electroconductivity is exhibited in the direction in parallel to the film surface. At the same time the long chain alkyl group constituting the hydrophobic site forms an insulator portion. Accordingly, the built-up film thus formed on a substrate is characterized by electroconductive layers and insulating layers laminated alternately.
When the film structure is, analyzed electrically for example, as shown in FIG. 11, the electroconductive regions 14 due to the hydrophilic site and the insulating regions 13 due to the hydrophobic site are repeated alternately in the built-up direction (the direction perpendicular to the film surface of monomolecular built-up film 20 on the substrate 12). This electroconductive monomolecular built-up film is noteworthy from the viewpoint of its application for electronic devices or in the development of molecular electronics, or to bioelectronics as a ultra-thin film electroconductor exhibiting great anisotropy in electroconductivity.
In the application of such organic electroconductive materials to wiring materials, or as electronic device materials, a technique is essential for manipulating the electroconductive thin film to form an electroconductive region with any desired shape (patterning technique).
Patterning techniques of the prior art can be roughly classified into two categories of methods, one being the method to effect selective growth of film only in the desired region, and the other being the method in which a pattern is formed by a post-treatment after film formation.
Although the LB method of forming a monomolecular film provides means for easily forming an extremely uniform film with respect to the film surface direction on the substrate having the monomolecular layer transferred thereon, it is very difficult to selectively grow the monomolecular built-up film on such a substrate. It is for this technical reason that practical application of the LB method is limited in spite of a large number of investigations. Accordingly, post-treatment is advantageous in pattern formation of a monomolecular built-up film. Methods for changing electrical characteristics of the film by post-treatment of monomolecular built-up film, are known. For example an iodine-doping method (Mol. Cryst. Liq. Cryst., 120 (1985) 319) is known electroconductivity is increased.
A change in electroconductivity is also reported to occur together with a change in light absorption characteristics of a dye film by acid or alkali treatment (Thin Solid Films, 129 (1985) 15).
However, all of these methods relate to post-treatments of the entire film, and they are not intended for application to electronic device materials as mentioned above.
Of course, if a desired region of a monomolecular built-up film could be removed from the substrate, a desired electroconductive pattern would be formed, and there would be possibility to realize this according to the chemical etching method which has been used in a variety of technical fields, typically in inorganic semiconductors. However, a masking material, a masking method, and an etchant (an etching solution) cannot easily be selected, and also the selection depends greatly on the kind of the molecule constituting the film and therefore there is no generally applicable way. In addition, such method is not suitable for fine working, and uniform working on a large area cannot easily be done, and therefore it is limited in uses as the working technique.
On the other hand, various methods have been known for preparing print wiring, but in the case of preparing fine wiring on a metal thin film such as of copper, aluminum, etc., the problem arises in the point of necessity of large number of steps of (1) vapor deposition of metal on the substrate, (2) coating of photoresist, (3) exposure to light, (4) developing, (5) etching, (6) removal of resist. Wiring members for bioelectronics could not be prepared by such a method, because substrate shall be heated on vapor deposition of a metal.
On the other hand, for providing an electrode onto an electroconductive film, there have been known, for example, the following methods: [1] a method in which an electrode pattern is provided previously on the substrate for lamination of an electroconductive film thereon and then an electroconductive film layer is formed thereon; [2] a method in which an electrode pattern is directly formed on an electroconductive film; [3] a method in which a probe is contacted with electroconductive film, or an electrode in a blade shape is pressure contacted with the film; and [4] a method in which an electroconductive paste is coated on the electroconductive film.
In the electroconductive film formed of a monomolecular built-up film having electroconductive layers and insulating layers laminated alternately, conductivity in the direction of the normal line of the film surface is extremely low, and current can flow through only one layer of the electroconductive layer exposed on the film surface according to the above methods [1] and [2], whereby other electroconductive layers could not be utilized as current passages. With the methods of [3] and [4], all of the electroconductive layers can be utilized as current passages, but mechanical breaking of the film or chemical breaking of film with solvents, etc., are sometimes caused. Further, since the terminal ends of the respective electroconductive layers in contact with electrodes are formed thinly, they cannot sufficiently contact the electrodes, and in some cases incomplete conduction occurred due to failure of contact of a part of electroconductive layers with electrodes.
Also, as a method (5), in conventional bulk or inorganic thin films, as shown in FIG. 12, said thin film 21 is provided on the substrate 12 and electrodes (metal layer such as Au, Cu, Al, etc.) 10 are provided on (see FIG. 12A) or beneath (see FIG. 12A) the surface of said thin film 21, whereby electrode formation such as ohmic or Schottky junction etc., can be effected. However, when the above method [5] is applied to the organic thin film having electrical anisotropy as described above, due to the presence of insulating layer between each electroconductive region and electrode, it is difficult to form electrodes such as ohmic or Schottky junction, etc.
Very few methods for providing electrode onto organic materials having such electrical anisotropy can be found in the prior art, and also they have been poor in controllability of electrode shape, etc. For example, in the case of measurement of conductivity in the planar direction of a monomolecular built-up film comprising bis-tetracyanoquinodimethane docosylpyridinium as mentioned above, a part of the monomolecular built-up film 20 built up on the glass substrate 12 as shown in FIG. 13 is mechanically destroyed or peeled off, and a conductor is filled at the site to provide thereby external connecting electrodes 22 for said built-up film. Specifically, it is applied by rubbing an electroconductive paint (e.g. silver paste, etc.) against said monomolecular built-up film, and the state electrodes provided is as shown in FIG. 13.
However, according to the method for equipment of electrodes as described above, the electrode portion is not necessarily regular but rather uneven as shown in FIG. 13, whereby it is difficult to control precisely parameters influencing greatly the electrical characteristic such as inter-electrode distance or electrode area, and of course reproducibility is also poor. Also, when application to semiconductor devices, etc., is considered, minute working technique is necessarily demanded, but the above method is not suited for this purpose at all. Further, as in coating of an electroconductive paint including a step of contact of an organic solvent with monomolecular built-up film, there may be the influence of the solvent, namely film dissolution or film structure change at the coated portion or the vicinity thereof, sometimes leading to deterioration of device characteristics such as lowering in conductivity during equipment of electrodes.